1. Field of the Invention
The present invention relates to improvements of a thermal transferring printing method, and it particularly relates to a thermal transferring printing method suitable to a recording medium of which a surface has unevenness to print thereon.
2. Description of the Related Art
As is well known, a thermal transferring printing apparatus is used to print an ink pattern such as a picture or letters on a recording medium by thermally transferring hot-melt or hot-sublimable ink coated on an ink sheet to the recording medium by heating the ink sheet with a thermal head. However, it poses a problem that a recording medium having surface unevenness (rough surface) can not be employed in the apparatus because of degradation of printing quality due to an insufficient contact of the ink with the recessed portions of the unevenness of the recording medium.
As countermeasure of the insufficient contact, a hot-melt ink having high fluidity or a dot plate formed in accordance with the printing contents is employed as well as applying a large contact force with the thermal head. However, an acceptable result is not obtained yet.
In order to eliminate the above problem, there is proposed a thermal transferring printing method in "Japan Hardcopy '92", as shown in FIG. 1.
FIG. 1 is a side view showing a general construction and an operation of a thermal transfer printer in a prior art.
Referring to FIG. 1, after thermally transferring an ink pattern 101 onto a surface of a soft platen roller 103 from an ink sheet 100 with a thermal head 102, the ink pattern 101 on the platen roller 103 is printed by pressing the platen roller 103 onto a surface of a recording medium 104 having an uneven surface to be printed.
In the above method, however, when using high fluidity ink, there are problems that the ink is liable to flow out from the printed ink pattern on the recording medium when the recording medium has a smooth surface in particular, and it is difficult to superpose many colors of ink on the recording medium at the same time. In addition, a printing of a picture having gradation is also difficult.